INITSEG     equ 0x9000
SYSSEG      equ 0x1000
SETUPSEG    equ 0x9020

    cli     ; 保护模式下中断机制尚未建立，应禁止中断

start:    
    mov ax, SETUPSEG
    mov ds, ax
    lgdt    [gdt_48]

    mov al, 2
    out 0x92, al

    mov ax, 0x0001
    lmsw    ax
    jmp $

gdt:
    dw  0, 0, 0, 0
    dw  0x07ff, 0x0000, 0x9a00, 0x00c0
    dw  0x07ff, 0x0000, 0x9200, 0x00c0

gdt_48:
    dw  0x800
    dw  512 + gdt, 0x9